Use SubFormState from Core

Problem/Motivation

There is a SubFormState provided by Core. There is a \Drupal\authorization\Form\SubFormState

Steps to reproduce

Proposed resolution

Use the SubFormState provided by core. Looks to have been around since 8.9

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Form%21Su...

Remaining tasks

User interface changes

API changes

Data model changes